Radio noise rejector circuit



March 30, 1948. D. L. HINGS 2,438,501

RADIO NOISE REJ ECTOR CIRCUIT Filed Aug. 21, 1942 7 g I v I &

RECEIVER DETECTOR AND [U INPUT RECEIVER OUTPUT SCREEN A ATTO EYS Patented Mar. 3.0, 1948 RADIO NOISE REJECTOR CIRCUIT Donald L. Hings, Ottawa, Ontario, Canada, assignor to Electronic Laboratories, Inc., Indianapolis, Ind., a. corporation of Indiana Application August 21, 1942, Serial No. 455,629 In Canada August 20, 1942 My invention relates in general to a radio receiver and more particularly to a radio noise rejector for the radio receiver.

An object of my invention is to suppress undesirable noises and interferences in radio receivers thereby clarifying the desired signal.

Another object of my invention is to obtain increased sensitivity or gain of a, radio amplifier with a rejector circuit thereby eliminating additional amplifiers.

Another object of my invention is to reject undesirable noises and interferences in a radio receiver by using no more tubes than that required in existing radio receivers having substantially an equal sensitivity.

Another object of my invention is to reject electric spark interferences on fading radiotelephony signals with a minimum of distortion in the received signals.

Another object of my invention is to use a rejector circuit as an integral part of radio frequency amplifier system.

Another object of my invention is to use a rejector circuit as a radio frequency amplifier in advance of the detector and receiver output.

Another object of my invention is to provide for the suppressing of undesirable noises and interferences in a radio receiver by isolating the interference noise waves and then subjecting the isolated interference noise waves upon a control element of an amplifier tube to cause the tube to suppress the amplification of the incoming interference noise waves which are being impressed upon the amplifier tube and which would normally be amplified.

Another object of my invention is to suppress noises in an amplifier circuit by using the noise energy to control the operation of an amplifying tube in the amplifying circuit for the duration of the existence of the noise without substantially affecting the amplitude of the amplified envelope of the incoming signal modulated carrier waves.

Another object of my invention is to provide for increasing the selectivity, and the sensitivity or gain of an amplifying tube, as well as to cause the tube to operate to suppress the noise waves for the duration of their existence without substantially afiecting the amplitude of the amplified modulation envelope of the incoming signal modulated carrier waves.

Another object of my invention is to reduce the amplitude of the noise waves to a value which substantially coincides with the amplitude of that portion of the signal modulation envelope where the noise Waves occur.

9 Claims. (01. 250-20) Other objects and a fuller understanding of my invention may be had by referring to the following description and claims, taken in conjunction with the accompanying drawing, in which:

Figure 1 is a diagrammatical illustration of a radio noise rejector embodying the features of my invention:

Figure 2 is a fragmentary view of my radio noise rejector showing a modification in certain partsthereof.

With reference to Figure 1 of the drawing, my radio noise rejector is subjected to incoming signal modulated carrier waves and electric interference waves from a radio receiver input indicated generally by the reference character 9. The output of my noise rejector circuit is arranged to supply energy to a detector and receiver output indicated generally by the reference character 8. The receiver input 9 and the detector and receiver output 8 may comprise any known or existing circuits. The electric interference waves consist principally of high amplitude, short duration radio-frequency oscillations and may be produced either by such natural causes as lightning; that is static, or by such man-made devices as electrical appliances, ignition systems of airplane and automobile motors, and other devices. The interference producing waves from these sources are distributed throughout the entire frequency range used in radio communication and present a difficult problem to solve.

My noise rejector circuit comprises generally an output amplifier tube It, a rejector driver amplifier tube 54, and a dual diode-triode tube which functions as a detector and a true noise amplifier. The output amplifier tube l6 may be of any suitable existing type and, as illustrated, comprises a plate I! for supplying energy to the detector and receiver output 8, a control grid l9 connected to receive energy from the receiver input 9, an injector grid I8 which operates in conjunction with the control grid I9 for suppressing the noise, a filament 20, a screen grid l2, and a suppressor grid I 3 which is connected to an indirectly heated cathode l4, heated by the filament 20. The control electrode 19 is maintained at a negative potential with respect to the oathode 4 by employing a conventional cathode bias resistor in which is shunted by a bypass condenser I l.

The rejector driver amplifier tube 54 may be of any suitable type and I find from actual practice that a radio frequency pentode amplifier tube such as illustrated works very satisfactorily.

This tube comprises a control grid 55 which is connected in parallel with the control grid IQ of the output amplifier tube It, a suppressor grid 56 which is connected to an indirectly heated cathode 58 heated by a filament 53, a screen grid 59, and a plate 51 which is connected to the upper end of the primary winding of the transformer 22 for supplyin amplified energy thereto. The tube 54 and the primary Winding lid of the transformer 22 together with the other component arts associated therewith maybe indicated generally by the reference character -"l and may be referred to as ;.a parallel amplifier.

section in relation to the output amplifier cube [6. The control grid 55 of the tube 5.4 .is sub,

waves and electric interference waves 'f nom the receiver input 9, and the tube functions to am- "'15 jected to incoming signal modulated -9flrrisr i :tiined circuits of the low audio frequency filter ..se ction 5 comprise respectively a filter audio'irequency 'choke and a fixed condenser 37, and a gfilter audio frequency choke S3 and a fixed condenser 51. The low audio frequency filter section 5 may :be for example adjusted to pass frzeqllellcies in excess of approximately 3000 cycles,

' which-means that audio frequencies appearing plify both the inco-ming signal modulatedlc-arrier' waves and the electric interference waves. The :ccptrQL-gfidtS is maintained at a negative poten- .tial with respect-to :the indirectly heatedcathode .58 Joy means :of a conventional-cathode bias resister 52 whichis shunted by-a bypass condenser gt. The :lower :end-of-thepri-mary winding of ithe i'.;r a .ns former1-22 is connected to the cathode 58 by means of a plate bypass condenserii-fi. The iscreemgrid ;59-is-also bypassed to the-cathode 53 ab)! a screen bypass condenser :50. A screen voltage dropping resistor il is connected in series with the screen grid :59 --,;to limit the screen' grid current. A plate isola ing tor iii isconnected i'betweemthe lower end of {the primaryiwinding A; :of the t ansformer andw he p tive potential lead 'is connected to oneterminal of the detector and receiver (output 8. The primary .winding '44 .ofthe transformer 22 is tuned to resscheme at :the carri freq en y .by ns of an adjustable "tunin condenser :45 which is .cgn- :nected across the primary winding 44.

Ff-he .a1n plified signal modulated ,carrier waves and the amplified electric interference 'waves which ,pass through the primary winding M of the transformer 22 are transformed to .the secondary winding .43-of the transformer 22 where sins 4,3 fortuningthe circuit to :resonanceat-the carrier-frequency; The first of the seriesofitreat- ,ments maybe e cribed as adetectin treatment :vrbich is vfor detectineth si nal modulated car- ;rier waves and the interference vvas es supplied from :the .output of the reilector d iv r amp ifier tube :54 :tothe transformer '22,. The ;.detecting equipment comprises the rectifyin i de' plate wzcand the (3ath0dl313i, the bypass capacitor :46,

'tthe-wfixed filter resistor Jiil, the bypasscapacitor i9 an -the volume control :i'esistor v552;. iI-he capac tor 4.5;. the iix d filter r sistor All and t capacitor 7 t9 zremoves the -radio frequency I Z Qm both the si nal m dulat d carrier waves :and th electric interferen e waves :with the result that currentrepresenting the modulation envelope of 70 the rectified signal and interference waves only "fiowthnough'thevolume control resistor v:38.

f'The =next operation in the 1 series .of treatments isitos-filter .cut the lower frequencies :o f the detectedsignal waves andi'electric interference waves below this value such as those Within the vocal range ar e filtered out of both the detected signal waves and the electric interference waves. I find from experience that substantially all interference waves have .a frequency in excess of 3000 cycles per second. This enables my low audio frequency filter section ,5 .to isolate the lower band "of the frequencies :of the detected signal waves from the interference waves, which are transferred to the control grid 26 of the dual .diode-triode tube through means of acoupling .condenserEZ. r r

The amplification of the isolated electric in- Aterferencewaves and the subjection of these amplified .waves on the injector grid 18 comprises :the next .operation in thisseries of treatments. The amplification of the isolated electric interference Waves is effected by the 'triode elements :of the tube 2 which comprise aplate 25,'a con .trOlegrid 26 which receives'isolated electric inter- ,ference waves from the low audio frequency filter section 5, and an indirectly heated cathode '35 which is heated by a filament 30. The control grid 26 is maintained-ate negative potential with respect to the cathode 3! by means of a conventionalcathode resistor 32 which is shunted by means-of la cathode bypass condenser 33. The controlgrid 2B is connected to ground by means -.of grid resistors '34 and 32. l The 'tri'ode elements of the tube 21 function as a coupling unit, together-With the coupling condenseri23 toimpress the amplified isolated electric interference waves from the plate .25 of the'tube'zl upon the injector grid l8 of the tube 16. Y The coupling tube ele- .ments and the associated partsmay be indicated generally by the reference character 0 and may be referred to as amplifying coupling means. The plate 25 maybe connected to the positive lead that goes to the detector and receiver output -;.8' through means of aplateload resistor 23. The amplified isolated electric interference waves which are impressed upon the injector grid lt function-to cause the tube into suppress theiam- .,pli-fication of the incoming electric interference -.-waves-from the receiver input e without substan- ;tially aifecting the amplitude of the amplified V vlnodulatedenvelope of the incoming signal modulation carrier waves. iThat is to say, the amplified isolated electric interference noise waves modifies the-bias of the injector grid i0-so that the. amplitude of the electric interference waves is -1imited f or the duration of their existence. I find from practice that by adjusting the volume cjontrolresistortfl, I'am able to make thea'mpli- V tilde of the electric interference waves which are passedby the tube l 6 to be substantially the same :as'theamp'litude of that portion-of the modula- 7 tion envelope where the electric interference waves occur in the envelope. In other words, the amplitudes of the electricinterference waves for the duration of their existence follow the general pattern of the amplified modulation envelope of the signal modulated carrier waves. In my invention, the suppression of the electric interference waves occurs only during the interval of their existence and accordingly the suppression action does not modify or afiect the general amplitude or pattern of the amplified modulation envelope of the incoming signal modulated car rier waves.

Another treatment which is imposed upon the output energy of the rejector driver amplifier tube deals with the fact that I transfer energy from the rejector driver amplifier tube to the injector grid l8 to increase the sensitivity and gain of the amplifier tube l6. This is one reason why I refer to the tube 54 as a rejector driver amplifier tube, in that the tube 54 co-operates with the tube It to cause the tube it to have a larger gain, which thereby enables me to obtain increased sensitivity with my rejector circuit, thereby eliminating additional amplifiers. In addition, the selectivity of the amplifier output tube is is sharpened by the cooperative action between the tubes I6 and 54. The driving power from the tube 54 is conveyed to the injector grid l8 of the tube It through means of a radio frequency coupling condenser 4| which leads to the control grid 25 of the tube 21 where the coupling action of the radio frequency is amplified and then impressed upon the injector grid H3. The capacitor 4| feeds radio frequency energy of a reduced amplitude to the grid 26 of the tube 27. The ca 1 pacitor 46 is connected at the radio frequency end of the radio frequency filter, which means that the capacitor 46 is located in that part of the filter system which is connected next to the radio frequency transformer is and as a result the capacitor 46 does not filter out all of the radio frequency energy supplied by the transformer 43. That part of the radio frequency energy which is not filtered out is finally filtered out by the capacitor 39 and the resistor 40. Consequently the driving power from the tube 54 is conveyed to the injector grid l8 of the tube I6.

In the event that the interference wave is abnormally strong over and above the setting of 'the volume control resistor 38, I still provide for the suppression of the excessively strong noise by means of a noise biasing resistor 2| which is connected in circuit relation with the injector grid l8 and the diode element 28 of the tube 21, so that when current flows through the resistor 2| the general level of the bias of the injector grid I8 is shifted. Thus, for example, upon an increase in current flow through the resistor 2|, the level of the bias of the grid I8 becomes more negative and causes an increased amount of suppression action against the passage of electric interference waves through the tube Hi.

In as much as the tube It; is aided by the rejector driver amplifier tube 54 to effect a large sensitivity or gain, I therefore amplify the isolated electric interference waves passed by the low audio filter section 5, so that the action of the injector grid 8 is sufficiently great to suppress substantially all of the incoming electric interference waves, notwithstanding the fact that the output amplifier tube I6 is operating with a large gain.

In Figure 2 I show a modified form of coupling the secondary winding 43 of the transformer to the injector grid N3 of the tube H5, in that I inthan the diode anodes 28 and 29, which cuts ofi rectification of the noise at any desired amplitude by adjustment of the resistor 32 which in Figure 2 is shown as an adjustable resistor, without substantially afiecting the amplitude of the signal modulation envelope of the incoming signal modulated carrier waves. By this arrangement there is always an upper limit to the sound level of the noise which may always be relied upon regardless of the amplification of the modulation envelope of the carrier wave input. The condenser 66 couples the low audio frequency filter section 5 to the detector circuit.

In my invention, all the noises having a frequency above the setting of the low audio frequency filter setcion 5 are suppressed without imposing a limit upon the amplitude of the signal modulation amplitude of the carrier waves. The noise waves may be suppressed even though they may have an amplitude lower than the peak signal modulation amplitude of the carrier waves. When the noise waves are suppressed, the am plitudes thereof may be brought down to a level that substantially coincides with that portion of the signal modulation envelope where the noise occurs. Since the noise waves are separated from the detected signal waves, I am able to control the interference waves independently of the signal modulation amplitudes of the carrier waves. The suppression action of the noise waves may vary in proportion to the amount that the noise peaks extend above the signal modulation envelooes, and not necessarily upon the noise level itself.

Although I have shown and described my invention with a certain degree of particularity, it is understood that changes may be made therein without departing from the spirit of the invention which are included within the scope of claims hereinafter set forth.

I claim as my invention:

1. In a radioreceiver subjected to incoming energy waves, the improvement of circuit means for amplifying the said energy waves comprising, in combination, a first amplifier tube arranged to supply a load circuit and having at least a control grid and a second grid, a second amplifier tube having at least a control grid, the control grids of said tubes receiving said incoming energy waves, said second tube amplifying said incoming energy waves, connection means between the second tube and the second grid for impressing the amplified incoming energy waves upon the second grid in substantially an in-phase relationship to the incoming waves to increase the sensitivity and the gain of the first amplifier tube, and biasing means for the second grid responsive to the amplitude of the amplified energy waves impressed upon the second grid to shift the bias of the second grid for governing the action thereof.

2. In a radio receiver subjected to incoming carrier waves and lectric interference waves, the

improvement of an interference rejector circuit comprising, in combination, a first amplifier tube arranged to supply a load circuit and having at least'a control grid and aninjector' grid a secondamplifier tube having at least a control grid, the control grids of said tubes receiving the incoming carrier waves and the electric interference waves, said second tube amplifying said incoming carrier waves and the electric interference noise waves, connection means between the second tube and the injector grid for impressing the amplified incoming carrier waves and the electric interference waves upon the injector grid in substantially an inphase relationship to the incoming carrier waves to increase the sensitivity and the gain of the first amplifier tube, detector and filter means for substantially isolating the electric interfence waves from the carrier waves, and means connecting the detector and filter means to the injector grid for impressing the isolated electric interference noise waves upon the injector grid in substantially an opposing phase relationship to the incoming electric interference waves to suppress the electric interference noise waves.

3. In a radio receiver subjected to incoming carrier waves and electric interference waves, the improvement of an interference rejector circuit comprising, in combination, a first amplifier tube arranged to supply a load circuit and having at least a control grid and an injector grid, 9, second amplifier tube having at least a control grid, thecontrol grids of said tubes receiving the incoming carrier waves and the electric interference waves, said second tube amplifying said incoming carrier waves and'the electric interference waves, connection means for impressing the amplified incoming carrier waves and the electric interference waves from the second tube upon the injector grid in substantially an in-phase relationship to the incoming carrier waves to increase the sensitivity and the gain of the first amplifier tube, detector and filter means for substantially isolating the electric interference-waves from the carrier waves, means for impressing the isolated electric interference waves upon the injector grid in substantially an opposing phase relationship to the incoming electric interference waves to suppress the electric interference waves, and biasing means for the injector grid responsive to the amplitude of the energy impressed upon the injector grid to shift the bias of the injector grid for governing the action thereof.

4. In a radio receiver subjected to incoming signal modulated carrier waves and electric interference waves, an interference rejector circuit arranged to amplify the amplitude of the signal modulated carrier waves and to suppress the electric interference waves for the duration of their existence, said interference rejector circuit comprising, in combination, a first amplifier tube arranged to supply a load circuit and having at least a control grid and an injector grid, a second amplifier tube having at least a control grid, the control grids of said tubes being connected in parallel and arranged to be subjected to the incoming signal modulated carrier waves and the electric interference waves, coupling means for impressing the amplified signal modulated carrier waves and the amplified electric interference waves from the second amplifier tube upon the injector grid in substantially an in-phase relationship relative to the incoming carrier waves 1 to increase the sensitivity and the gain of the first amplifier tube, detecting means connected to the second amplifier tube and including rectifying tube elements for detecting the amplified signal modulated'waves and thc:amplified electric infor impressing the amplified isolated detected electric interference waves upon the injector grid in substantially an opposing phase relationship relative to the electric interference waves for the duration of their eXistence'to-causethe first amplifier tube to suppress the amplification of the incoming electric interference waves.

5. In a radio receiver subjected to incoming signal modu-latedcarrier waves and electric interference Waves, an interference rejector circuit arranged to amplify the amplitude of the'signal modulated carrier waves and to suppress the electric interference waves substantially to the level of the modulation envelope for'the duration of th ir existence, said interference rejector circuit comprising, in combination, a first amplifier tube arranged to supply a load circuit:and'havingat' least a control grid and an injector grid,a second amplifier tube having at least a control grid, the control grids of said tubes being connected in parallel and arrangedto be subjected to'the incoming signal modulated carrier waves and the electric interference waves, regenerative coupling means for impressing the amplified signal modulated carrier waves and the amplified electric interference waves from the second amplifier tube upon the injector grid to increase the sensitivity and the gain of the first amplifier tube, detect,-

ing means connectedto the second amplifier-tube and including rectifying tube elements for detecting the amplified signal modulated waves and the amplified electric interference waves of the output of thesecond amplifier tube; thus pro-- ducing an amplified detected modulation envelope'comprising detected signal Waves and elec-,

tric interference waves, adjustable means for selectively varying the strength of the detected signal Waves and the electric interference waves, filtering means'for substantially filtering out of the amplified detected modulation envelope frequencies below approximately 3,600 cycles and thereby substantially isolating the detected electric interference waves from the detected signal waves, and coupling-amplifying means including amplifying tube elements for amplifying the isolated detected electri interference waves and modulation envelope. I

for degeneratively impressing the amplified isolated detected electric interference waves upon the injector grid for the duration of their existence toicause-the first amplifier tube to suppress the amplification of the incoming electric interference waves substantially to the level of the signal modulated carrier-waves and to suppress,

the electric interferencewaves'for the duration of their existence, said interference rejectorcircuit comprising, in combination, a first amplifier tube arranged to supply'a load circuit and having at least a control grid and an injector grid, a second amplifier tube having at least a control grid, the control grids of said tubes being connected in parallel and arranged to be subjected to the incoming signal modulated carrier waves and the electric interference waves, regenerative coupling means for impressing the amplifiedsignal modulated carrier waves and the amplified electric interference waves from the second amplifier tube upon the injector grid to increase the sensitivity and the gain of the first amplifier tube, said coupling means comprising coupling capacitor means and coupling amplifying means including amplifying tube elements, detecting means connected to the second amplifier tube and including rectifying tube elements for detecting the amplified signal modulated waves and the amplified electric interference waves of the output of the second amplifier tube, thus producing an amplified detected modulation envelope comprising detected signal waves and electric interference waves, filtering means for substantially filtering out of the amplified detected modulation envelope frequencies below approximately 3,000 cycles and thereby substantially isolating the detected electric interference Waves from the detected signal waves, and coupling amplifying means including amplifying tube elements for amplifying the isolated detected electric interference waves and for degeneratively impressing the amplified isolated detected electric interference Waves upon the injector grid for the duration of their existence to cause the first amplifier tube to suppress the amplification of the incoming electric interference waves.

'7. In a radio receiver subjected to incoming signal modulated carrier waves and electric interference waves, an interference rejector circuit arranged to amplify the amplitude of the signal modulated carrier waves and to suppress the electric interference waves for the duration of their existence, said interference rejector circuit comprising, in combination, a first amplifier tube arranged to supply a load circuit and having at least a control grid and an injector grid, a second amplifier tube having at least a control grid, the control grids of said tubes being connected in parallel and arranged to be subjected to the incoming signal modulated carrier waves and the electric interference waves, coupling means for impressing the amplified signal modulated carrier waves and the amplified electric interference waves from the second amplifier tube upon the injector grid in substantially an in-phase relationship relative to the incoming carrier waves to increase the sensitivity and the gain of the first amplifier tube, detecting means connected to the second amplifier tube and including rectifying tube elements for detecting the amplified signal modulated waves and the amplified electric interference waves of the output of the second amplifier tube, thus producing an amplified detected modulation envelope comprising detected signal waves and electric interference waves, filtering means for substantially filtering out of the amplified detected modulation envelope frequencies below approximately 3,000 cycles and thereby substantially isolating the detected electric interference waves from the detected signal waves, coupling amplifying means including amplifying tube elements for amplifying the isolated detected electric interference waves and for impressing the amplified isolated detected electric interference waves upon the injector grid in substantially an opposing phase relationship relative to the electric interference waves for the duration of their existence to cause the first amplifier tube to suppress the amp fi tion of the incoming electric interference waves, and adjustable means for selectively varying the sensitivity of the couplin amplifying means to limit the amplitude of the amplified isolated electric interference waves impressed upon the injector grid.

8. In a radio receiver subjected to incoming signal modulated carrier waves-and electric interference waves, an interference rejector circuit arranged to amplify the amplitude of the signal modulated carrier waves and to suppress the electric interference waves for the duration of their existence, said interference rejector circuit comprising, in combination, a first amplifier tube arranged to supply a load circuit and having at least a control grid and an injector grid, a second amplifier tube having at least a control grid, the control grids of said tubes being connected in parallel and arranged to be subjected to the incoming signal modulated carrier waves and the electric interference waves, detecting means connected to the second amplifier tube and including rectifying tube elements for detecting the amplified signal modulated waves and the amplified electric interference waves of the output of the second amplifier tube, thus producing an amplified detected modulation envelope comprising detected signal waves and electric interference waves, filtering means for substantially filtering out of the amplified detected modulation envelope frequencies substantially of the lower portion of the audio range and thereby substantially isolating the detected electric interference waves from the detected signal waves, coupling amplifying means including amplifying tube elements for amplifying the isolated detected electric interference waves and for degeneratively impressing the amplified isolated detected electric interference waves upon the injector grid for the duration of their existence to cause the first amplifier tube to suppress the amplification of the incoming electric interference waves, said amplifying tube elements of said coupling amplifying means including a diode anode with a load resistor connected thereto, said load resistor also being connected to said injector grid to act as additional biasing means upon passage of electron current by said diode anode.

9. In a radio receiver subjected to incoming signal modulated carrier waves and electric interference waves, an interference rejector circuit arranged to amplify the amplitude of the signal modulated carrier waves and to suppress the electric interference waves for the duration of their existence, said interference rejector circuit comprising, in combination, an amplifier tube arranged to supply a load circuit and having at least a control grid and an injector grid, regenerative coupling means for impressing signal modulated carrier Waves and electric interference waves upon the injector grid to increase the sensitivity and the gain of the amplifier tube, detecting means connected to receive the incoming waves for detecting the signal modulated carrier waves and the electric interference waves, thus producing a detected modulation envelope comprising detected signal waves and electric interference waves, filter means for substantially isolating the detected higher audio frequency electric interference waves from the detected lower finesse:

V 7 11. 7 12. 7 audio frequency signal waves, and degenerative o means for impressing the isolated detected elec- UNITED PATENTS trio interference waves upon the injector grid for be v N Date 7 the duration of their existence to cause the am- 7, ,1 9 I mficke Mar. 5, 1940 p1ifier-.to suppress the amplification of the in- 5 ,220, 3 Gab 5, 1940 coming electric interference waves. 2,237,457 Tellegen' Apr. 3, 1941 DONALD L. I-IINGS; 2,252,811 Lowell Aug. 19,1941

REFERENCES CITED i 7 o The following references are of record in the I V V file of this patent: 

